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Osmotic dehydration of red paprika was studied using a combined sucrose (5 to 45 g/100 g) and sodium chloride (0 to 15 g/100g) solution. The effective diffusion coefficients for water and solute were determined using the slope method based on the Fickian diffusion model. The effects of concentration of sucrose, sodium chloride and their complex interaction on water and solute diffusion coefficients as well as on equilibrium moisture and solid contents were studied using central composite rotatable design of experiments. The graphical optimization showed that at optimum conditions (sucrose concentration and sodium chloride concentration were 21.86 g/100 g and 2.02 g/100 g, respectively), the following criteria were achieved: water diffusion coefficient (D ew ) $ 0.80 x 10 -9 m 2 /s, solid diffusion coefficient (D es ) $ 0.82 x 10 -9 m 2 /s, equilibrium moisture content (m`) # 6.85 kg/kg, and equilibrium solid content (s`) # 2.00 kg/kg.

Rehydration kinetics of high-pressure pretreated (100, 300, and 500 MPa for 10 min) and osmotically dehydrated pineapple (Ananas comsus) cubes (2 × 2 × 1 cm) were studied at different temperatures (5, 25, and 35 °C), and compared with ordinary osmotically dehydrated samples. The effective diffusion coefficients for water and solute were determined, assuming the rehydration process to be governed by Fickian diffusion. Diffusion coefficients for water absorption into the tissue as well as for solute diffusion out of the tissue were found to be lower in the samples subjected to high-pressure treatment. Further, the diffusion coefficients decreased with increase in treatment pressure. A possible explanation for the observed decrease in diffusion coefficients can be attributed to the permeabilization of cell membranes, the release of cellular components, and structural changes of the cell materials. The diffusion coefficients were correlated with rehydration temperature (T) and treatment pressure (P) by an Eq. of the form D 5 A exp[2(B.P 1 C/T)], where A, B, and C are constants.

The proportion of intact, damaged, and ruptured (non-intact) cells (Zp) due to osmotic stress during osmotic treatment of potato was monitored using electrophysical measurement based on electrical impedance analysis. Osmotic stress on potato cell culture made cell membranes shrink thereby damaging the cells. The proportion of the ruptured and shrunk cells within the samples increased with the increase in concentration of solute in the osmotic solution. The osmotic removal of water from thin potato slices started at a critical osmotic pressure. Once the critical osmotic pressure was exceeded, mass transfer was rapid and the cells lost substantial amounts of water due to rupture of cell membranes.

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